Field of the Invention
The present invention relates to: an electro-photographic image forming apparatus that is provided with a print head serving as an exposing portion and including an array of multiple light-emitting elements extending in a main scanning direction; and a light intensity adjusting method for the image forming apparatus.
Description of the Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
As is well-known, the light intensity of a light-emitting element used in such an image forming apparatus as described above decreases because light-emitting elements are degraded with their cumulative light emission times. The light-emitting elements have different cumulative light emission times because documents to be printed are frequently put at different positions in a main scanning direction. This means, the light-emitting elements normally do not have the same degradation level on light intensity. The light-emitting elements emit light at different light intensities, causing the unevenness of toner density in a developed image. That is the reason that conventional image forming apparatuses are configured to adjust the light intensities of all the light-emitting elements at a certain time, e.g., before a document is exposed to light. This is called light intensity adjustment in this Specification.
One of the conventional image forming apparatuses is, for example, an electrographic apparatus described in Japanese Patent Application Laid-open Publication No. 2003-334990. This conventional image forming apparatus is provided with an exposing portion including an array of multiple light-emitting elements extending in a main scanning direction; it generates an electrostatic latent image on the surface of a photoconductor rotating while being charged, by controlling the turning on and off of all the light-emitting elements.
The image forming apparatus counts up how many times each light-emitting element has been turned on, and unnecessarily repeats turning on the light-emitting elements other than the light-emitting element having been turned on the most times. Accordingly, as described in Japanese Patent Application Laid-open Publication No. 2003-334990, the degradation conditions of all the light-emitting elements are adjusted to the same level, and light intensity adjustment is performed without complexity.
Also, as described in Japanese Patent Application Laid-open Publication No. 2003-334990, the degradation conditions of all the light-emitting elements are adjusted to that of the light-emitting element having been turned on the most times. Accordingly, the light-emitting elements are degraded unnecessarily fast, making the lifetime of the exposing portion short.